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performed assuming a waste height of 148 feet. The construction drawings for the construction of Module 1 show that 3 -inch diameter, SDR 15.5, perforated, HDPE pipes were used in this module. The construction drawing show a sand bedding material below the pipe and gravel drain rock around the pipe. To be conservative, it is assumed that the entire bedding material consists of sand. The pipe loading calculations are presented in Attachment E. These calculations show that the existing pipes in Module 1 can support the proposed waste final grades shown in Figure 2 with adequate factors of safety against ring deflection, wall buckling, wall crushing, and circumferential strain. 6.2.2 Existing Leachate Pipes in Module 3 The construction drawings for the construction of Module 3 show that 4 -inch diameter, SDR 15.5, perforated, HDPE pipes were used in this module. The construction drawing show a sand bedding material below the pipe and gravel drain rock around the pipe, similar to Module 1. Again, to be conservative, it is assumed that the entire bedding material consists of sand. The existing maximum waste height above the critical leachate pipe within Module 3 is approximately 135 feet. The conceptual final grading plan for the proposed vertical expansion showed a maximum waste height of 195 feet above the most critical leachate collection pipe within Module 3. The initial pipe loading calculations showed that the pipe will not able to support this waste height. Therefore, additional pipe loading calculations were performed to determine the maximum waste height that the pipes in Module 3 can support. These calculations (see Attachment E) show that the leachate collection pipes in Module 3 can support a maximum waste height of 165 feet. The final grading plan has been revised accordingly and the final grades shown in Figure 2 reflect this revision. 6.2.3 Existing Leachate Pipes in Module 4 Based on the previously approved final grading plan for the landfill, the maximum waste height above the most critical leachate collection pipe within Module 4 is 130 feet. The proposed vertical expansion will increase the maximum waste height above the most critical leachate collection pipe in Module 4 to approximately 241 feet. Therefore, the existing leachate collection pipes in Module 4 have been checked for a maximum waste height of 241 feet. The construction drawings for the construction of Module 4 show that 4 -inch diameter, SDR 15.5, perforated, HDPE pipes were used in this module. The construction drawings also show a gravel bedding material both below and around the pipe. The pipe loading calculations included in Attachment E show that existing pipes in Module 4 can support the proposed waste height in Module 4 with adequate factors of safety against ring deflection, wall buckling, wall crushing, and circumferential strain. Since the long-term factor of safety against wall crushing is very close to the required Geotechnical Analyses for NCRCSL Department of Public Works/Solid Waste Shaw Environmental, Inc. County of San Joaquin, December 12, 2007 6-2